Pap smears are routine tests that doctors use to screen patients for signs of cervical cancer. Before they were widely adopted in the late 1950s, the disease was a leading cancer killer of women. According to the U.S. National Institutes of Health, Pap testing has helped curb cervical cancer deaths by more than 60 percent.

To perform a Pap test, a doctor swabs some cells from a woman's cervix and sends them to a lab, where they're examined under a microscope by a pathologist. The cost for that service is normally between $20 and $30.

So Dr. Cheryl Bettigole, a family physician in Millville, N.J., was initially caught off guard when some of her patients called to complain that their bills for their Pap smears were hundreds of dollars more than she, or they, had expected.

Not anymore. "These days," she wrote in an article published in the Oct. 17 issue of the New England Journal of Medicine, "I am no longer surprised to find laboratory charges of $1,000 or more."

"The doctor's office is the only place I know of where we tolerate this lack of transparency," Bettigole said in an interview. "You don't go buy shoes and say, 'I wonder how much they're going to cost when I look at my Visa bill.' "

"It has a really serious impact on people," she said. "I've had patients turn down all sorts of testing or they won't go to the hospital if they need to go because they're afraid of the bill they're going to get."

Why have bills for such a routine test suddenly spiked? Bettigole did some checking. She found out that it's not the Pap test itself that's usually the big-ticket item. For women who have insurance, Pap tests involve no out-of-pocket costs to patients under the Affordable Care Act.

Instead, she said, it is other tests that laboratories have promoted to doctors along with Pap smears that drive up the price. For example, many labs offer to check for sexually transmitted diseases such as chlamydia and gonorrhea along with a Pap smear. They will also look for the Trichomonas parasite or specifically identify the exact species of yeast found in a sample.

Although there are certainly some cases in which it would make sense to test for those kinds of infections, Bettigole said it's not appropriate to check for them in every case.

"There's no real reason why we need to identify a strain of yeast," she said. "You can diagnose yeast by looking under the microscope. If you see yeast, you treat yeast. I don't need to know what strain. But labs will often charge a huge rate for telling me that."

And Bettigole said it's all too easy to check the box for one of the combination tests on an order form, instead of a plain Pap. She said most doctors have no idea how much all those tests can inflate the tab and harm patients.

A large part of the problem is that labs don't charge set prices for their tests. They typically charge their highest rates to uninsured patients and lower rates to patients who have insurance companies negotiating on their behalf. And even prices for insured patients vary by insurance company, one expert said.

"Oftentimes, their negotiated contracts with rates vary between insurers, so there's not simply one price per test," said Scott McGoohan, vice president of reimbursement and scientific affairs for the American Clinical Laboratory Association.

That makes it difficult for doctors and patients to find out ahead of time what a test is going to cost.

"Laboratories don't order the tests they perform. We are a third-party contractor who is hired to do a service," he said. "As the article itself indicates, a large part of the responsibility lies at the physician's pen and what they choose to order."

For its part, the American Congress of Obstetricians and Gynecologists (ACOG) said it's working to make sure doctors are better educated about the tests they order.

"ACOG is concerned when we become aware of excessive health care charges, particularly to a vulnerable public," the organization said in a statement about Bettigole's article. "ACOG is working hard to develop educational resources for our fellows and residents-in-training to increase awareness about the costs and appropriateness of many interventions, including diagnostic tests."